Project Summary ? Abstract A fundamental challenge of external beam radiation treatment is that the internal tumor target is not directly visible during treatment. The lack of an efficient imaging technology to monitor beam path and patient anatomy is a significant weakness that limits treatment accuracy, and as a consequence precludes the effective use of radiotherapy in many cancers close to vital organs. This deficiency is particularly problematic for lung cancer patients, as lung tumors often are subject to respiratory-induced motion. This project aims to develop a real-time imaging system for monitoring the treatment target and beam positions in stereotactic ablative radiotherapy (SABR) of lung cancer. Once successfully developed, this technology can be applied not only to lung cancer patients receiving SABR treatment but also to other cancer patients receiving radiation therapy. Over 60% of cancer patients (about 990,000 in the US) receive some form of radiation therapy each year. The proposed research is significant, because it is expected to advance technology and improve the treatment effectiveness for a large population of cancer patients receiving radiation therapy. To address this challenge, we propose to develop a novel imager to confirm patient alignment and to monitor the patient during treatment in real-time. Our proposed back-scatter imaging technology utilizes the scatter radiation produced by the treatment beam; thus it provides treatment confirmation images without incurring additional radiation dose or potential side effects. In addition, as scatter radiation is present continuously during treatment, these images can be produced in real-time. This approach is innovative, because it utilizes a naturally occurring byproduct from radiotherapy and improves both accuracy and safety of this type of treatment. This project is intended as the feasibility study for this technology for image-guided radiation therapy applications in clinical practice. The specific aims of the project are: (1) Design a pinhole-camera type imaging system that can be integrated into a commercial external beam radiation therapy system. The system design will include pinhole-camera configurations and requirements for a flat-panel type x-ray detector. (2) Build and use appropriate phantoms containing simulated tumor and lung materials as test treatment subjects to optimize the imaging system. Our results will provide guidelines for the design of a clinical system. While the immediate focus of the current proposal is to design a novel scatter imaging device for SABR treatment of lung cancer patients, our long-term objective is to use this type of device to improve the accuracy of radiation treatment of cancer in general; this will allow patient-specific adaptive therapy and improve the treatment outcome. The data obtained from this proposed R21 feasibility study will form the basis for a follow up R01 grant application to the NIH.